I believe the answer from Hillsborough is correct. When I was trying to resolve the problem with PayPal the customer representative suggested I contact my mobile provider because "I do know you need to have Premium Txt Messaging set up with your phone company to receive texts from 6-digit numbers. I know I hadto call my phone provider to enable this for me".

Thank you Hillsborough for corroborating the information I received from PayPal.